The existence of binary supermassive black holes ( SBHs ) is predicted by models of hierarchical galaxy formation .
To date , only a single binary SBH has been imaged , at a projected separation of 7.3 parsecs .
Here we report the detection of a candidate dual SBH with projected separation of 0.35 pc in the gas-rich interacting spiral galaxy NGC 7674 ( Mrk 533 ) .
This peculiar Seyfert galaxy possesses a \sim 0.7 kpc Z-shaped radio jet ; the leading model for the formation of such sources postulates the presence of an uncoalesced binary SBH created during the infall of a satellite galaxy .
Using very long baseline interferometry ( VLBI ) , we imaged the central region of Mrk 533 at radio frequencies of 2 , 5 , 8 and 15 GHz .
Two , possibly inverted-spectrum radio cores were detected at 15 GHz only ; the 8 - 15 GHz spectral indices of the two cores are \geq - 0.33 and \geq - 0.38 ( \pm 30 \% ) , consistent with accreting SBHs .
We derive a jet speed \sim 0.28 c from multi-epoch parsec-scale data of the hotspot region , and a source age \geq 8.2 \times 10 ^ { 3 } yrs .